PLASTICS. Characterization and Failure Analysis of.

Characterization and Failure Analysis of PLASTICS

Copyright 2003 by ASM International All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the written permission of the copyright owner. First printing, December 2003 Great care is taken in the compilation and production of this book, but it should be made clear that NO WAR- RANTIES, EXPRESS OR IMPLIED, INCLUDING, WITHOUT LIMITATION, WARRANTIES OF MER- CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, ARE GIVEN IN CONNECTION WITH THIS PUBLICATION. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM s control, ASM assumes no liability or obligation in connection with any use of this information. No claim of any kind, whether as to products or information in this publication, and whether or not based on negligence, shall be greater in amount than the purchase price of this product or publication in respect of which damages are claimed. THE REMEDY HEREBY PROVIDED SHALL BE THE EXCLUSIVE AND SOLE REMEDY OF BUYER, AND IN NO EVENT SHALL EITHER PARTY BE LIABLE FOR SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES WHETHER OR NOT CAUSED BY OR RESULTING FROM THE NEGLI- GENCE OF SUCH PARTY. As with any material, evaluation of the material under end-use conditions prior to specification is essential. Therefore, specific testing under actual conditions is recommended. Nothing contained in this book shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this book shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement. Comments, criticisms, and suggestions are invited and should be forwarded to ASM International. ASM International staff who worked on this project include Steve Lampman, Editor; Bonnie Sanders, Manager of Production; Nancy Hrivnak, Jill Kinson, and Carol Polakowski, Production Editors; and Scott Henry, Assistant Director of Reference Publications. Library of Congress Cataloging-in-Publication Data Characterization and failure analysis of plastics. p. cm. Collection of articles from ASM International handbooks. Includes bibliographical references and index. 1. Plastics Fracture. I. ASM International. TA455.P5C463 2003 620.1 9236 dc22 2003057732 ISBN: 0-87170-789-6 SAN: 204-7586 ASM International Materials Park, OH 44073-0002 Printed in the United States of America

Preface This book is collection of ASM Handbook articles on how engineering plastics are characterized and understood in terms of properties and performance. It approaches the subject of characterization from a general standpoint of engineering design, materials selection, and failure analysis. These basic activities of the engineering process all require clear understanding of plastics performance and properties by various methods of physical, chemical, and mechanical characterization. The first section introduces the fundamental elements of engineering plastics and how composition, processing, and structure influence their properties and performance. The second section contains articles on material selection and design, where the requirements of a plastic part are synthesized and analyzed in terms of function, shape, process, and materials. The next sections then cover the important physical, chemical, and mechanical properties of plastics. The last section covers failure analysis, which is the ultimate stage of characterization in the life of a part, but really only the penultimate stage in the overall engineering process. Failure analysis, in a broad sense, is another iteration of the design process, as it can provide important information on product and process improvements. Thus, it closely ties together with the characterization of properties and performance plastics during design and materials selection. This book would not have been possible without the original contributions from the authors of the Handbook articles. Thanks are extended to them. Steve Lampman May 2003 iii

Contents Introduction............................................. 1 Engineering Plastics: An Introduction.......................... 3 Polymer Structure...................................... 3 Chemical Composition and Structure...................... 9 Polymer Names...................................... 10 Properties of Polymers................................. 11 Engineering Thermoplastics............................. 19 Engineering Thermosets................................ 24 Effects of Composition, Processing, and Structure on Properties of Engineering Plastics..................................... 28 Composition......................................... 28 Thermal and Mechanical Properties....................... 38 Viscoelasticity....................................... 41 Properties of Engineering Plastics and Commodity Plastics.... 41 Electrical Properties................................... 42 Optical Properties..................................... 43 Chemical Properties................................... 44 Processing........................................... 44 Materials Selection and Design of Engineering Plastics......... 49 General Design Guidelines.................................. 51 Defining End-Use Requirements......................... 51 Part Geometry......................................... 51 Strength of Plastics.................................... 53 Cost Estimating Plastics Parts........................... 53 Stucture, Properties, Processing, and Applications........... 53 Design with Plastics....................................... 55 Mechanical Part Performance........................... 55 Manufacturing Considerations.......................... 55 Design-Based Material Selection......................... 60 Conclusions......................................... 62 Design and Selection of Plastics Processing Methods............. 64 Plastics Processing Methods.............................. 64 Injection Molding..................................... 64 Extrusion........................................... 66 Thermoforming...................................... 67 Blow Molding....................................... 68 Rotational Molding................................... 68 Compression Molding and Transfer Molding............... 69 Composites Processing................................. 70 Casting............................................. 72 Design Features and Process Considerations................ 72 Other Plastics Design and Processing Considerations......... 73 Materials-Selection Methodology........................ 73 Function and Properties Factors in Process Selection........... 75 Establishing Functional Requirements..................... 75 Properties Considerations and Processing.................. 75 Process Effects on Molecular Orientation.................. 77 Thermoplastic Process Effects on Properties................ 78 Thermosetting Process Effects on Properties................ 81 Size, Shape, and Design Detail Factors in Process Selection..... 83 Part Size Factors in Process Selection..................... 83 Shape and Design Detail Factors in Process Selection........ 83 Physical, Chemical, and Thermal Analysis of Plastics.......... 87 Physical, Chemical, and Thermal Analysis of Thermoset Resins.... 89 Chemical Composition Characterization................... 89 Processing Characterization............................. 94 Physical, Chemical, and Thermal Analysis of Thermoplastic Resins 105 Molecular Weight Determination from Viscosity........... 105 The Use of Cone and Plate and Parallel Plate Geometries in Melt Rheology.................................... 107 Chromatography..................................... 110 Thermoanalysis..................................... 112 Thermal Analysis and Thermal Properties..................... 115 Glass Transition Temperature............................ 115 Semicrystalline Polymers.............................. 115 Structural and Test Effects............................. 117 Moisture Effect on Tg................................ 119 Thermal Analysis...................................... 121 Differential Scanning Calorimetry....................... 121 Thermogravimetric Analysis........................... 122 Thermomechanical Analysis........................... 124 Thermal Properties..................................... 125 Determination of Service Temperature..................... 128 Service Temperature................................. 129 Thermal Properties of Thermoplastics...................... 131 Thermal Properties of Thermosets......................... 138 Low-Temperature Resin Systems....................... 138 Medium-Temperature Resin Systems.................... 140 High-Temperature Resin Systems....................... 141 Environmental and Chemical Effects......................... 146 Chemical Susceptibility................................. 146 Absorption and Transport.............................. 146 Additive Effects..................................... 147 Thermal Degradation................................. 147 Thermal Oxidative Degradation......................... 148 Photo-oxidative Degradation........................... 148 Environmental Corrosion.............................. 148 Chemical Corrosion.................................. 148 Degradation Detection................................ 148 Effect of Environment on Performance.................... 149 Plasticization, Solvation and Swelling.................... 149 iv

Environmental Stress Cracking......................... 149 Polymer Degradation by Chemical Reaction............... 150 Surface Embrittlement................................ 151 Temperature Effects.................................. 151 Characterization of Weather Aging and Radiation Susceptibility... 153 Degradation Factors.................................. 153 Test Methods....................................... 155 Flammability Testing..................................... 159 Fire Resistance of Polymeric Materials................... 159 Overview of the Burning Process........................ 159 Flammability Test Methods............................ 159 Electrical Testing and Characterization....................... 164 Electrical Tests...................................... 164 Electrical Properties of Plastics and Their Characterizations.. 171 Terminology........................................ 173 Optical Testing and Characterization......................... 177 Transmission and Haze............................... 177 Yellowness......................................... 177 Refractive Index..................................... 177 Birefringence....................................... 178 Surface Irregularity and Contamination................... 179 Surface Gloss and Color............................... 181 Ad Hoc Testing..................................... 181 Mechanical Behavior and Wear........................... 183 Mechanical Testing and Properties of Plastics: An Introduction.... 185 Tensile Properties.................................... 185 Other Strength/Modulus Tests.......................... 188 Creep Data Analysis.................................. 190 Dynamic Mechanical Properties........................ 191 Impact Toughness................................... 191 Hardness Tests...................................... 194 Fatigue Testing...................................... 194 Elastomers and Fibers................................ 194 Creep, Stress Relaxation, and Yielding....................... 199 Creep Failure....................................... 199 Stress Relaxation Failure.............................. 201 Yield Failure........................................ 201 Effect of Crystallinity................................. 202 The Aging of Polymers............................... 203 Crazing and Fracture..................................... 204 General Polymeric Behavior........................... 204 Ductile-Brittle Transitions............................. 204 Crazing............................................ 205 Fracture............................................ 206 Environmental Effects................................ 206 Initiation Criteria.................................... 206 Craze Growth....................................... 207 Effect of Crazing on Toughness......................... 207 Testing for Brittle Behavior............................ 207 Fracture Toughness Testing............................ 208 Fracture Resistance Testing................................ 211 Historical Development............................... 211 Fracture Test Methods for Polymers..................... 212 Impact Loading and Testing................................ 216 Material Considerations in Impact Response............... 217 Design and Analysis Techniques for Thin Plastic Components...................................... 228 Summary.......................................... 235 Fatigue Testing and Behavior.............................. 238 Fatigue Crack Initiation............................... 238 Fatigue Crack Propagation............................. 240 Factors Affecting Fatigue Performance of Polymers......... 243 Factography........................................ 247 Fatigue Failure Mechanisms............................... 249 Mechanisms of Fatigue Failure......................... 249 Thermal Fatigue Failure............................... 250 Mechanical Fatigue Failure............................ 251 Friction and Wear Testing................................. 259 Friction, Wear, and Lubrication......................... 259 Friction and Wear Test Methods........................ 260 Friction and Wear Test Data for Polymeric Materials........ 264 Wear Failures of Plastics.................................. 267 Interfacial Wear..................................... 267 Cohesive Wear...................................... 268 Elastomers......................................... 269 Thermosets......................................... 269 Glassy Thermoplastics................................ 270 Semicrystalline Thermoplastics......................... 270 Environmental and Lubricant Effects on the Wear Failures of Polymers...................................... 272 Summary and Case Study............................. 272 Failure Examples.................................... 274 Wear Failures of Reinforced Polymers....................... 276 Abrasive Wear Failure of Reinforced Polymers............ 276 Sliding (Adhesive) Wear Failure of Polymer Composites..... 282 Environmental Effects................................... 293 Thermal Stresses and Physical Aging........................ 295 Classification of Stress................................ 295 Thermal Stresses.................................... 296 Orientation Effects................................... 298 Physical Aging...................................... 299 Use of High-Modulus Graphite Fibers in Amorphous Polymers......................................... 302 Environmental Stress Crazing.............................. 305 Molecular Mechanism................................ 305 Environmental Criteria................................ 307 Material Optimization................................ 308 Testing............................................ 310 Moisture-Related Failure.................................. 314 Mechanisms of Moisture-Induced Damage................ 314 Effect of Moisture on Mechanical Properties.............. 319 Organic Chemical Related Failure........................... 323 Chemical Interactions................................. 323 Physical Interactions................................. 324 Photolytic Degradation.................................... 329 Sunlight........................................... 329 Polymer Photochemistry.............................. 331 Protection of Plastics from Sunlight...................... 333 v

Microbial Degradation.................................... 336 Biodegradation Mechanisms........................... 336 Biodeterioration and Biodegradation Definitions........... 337 Biodeterioration and Biodegradation Measurements......... 337 Experimental Example................................ 338 Failure Analysis of Plastics............................... 341 Analysis of Structure..................................... 343 Problem Solving..................................... 343 Molecular Spectroscopy............................... 343 Molecular Weight.................................... 346 Methods of Thermal Analysis.......................... 347 X-Ray Diffraction (XRD) Analysis...................... 353 Scheme for Polymer Analysis.......................... 354 Procedure for Analyzing Milligram Quantities of Polymer Sample................................... 354 Characterization of Plastics in Failure Analysis................ 359 Fourier Transform Infrared Spectroscopy................. 359 Differential Scanning Calorimetry....................... 362 Thermogravimetric Analysis........................... 363 Thermomechanical Analysis........................... 364 Dynamic Mechanical Analysis.......................... 365 Methods for Molecular Weight Assessment............... 366 Mechanical Testing.................................. 367 Considerations in the Selection and Use of Test Methods..... 368 Case Studies........................................ 368 Surface Analysis......................................... 383 Scanning Electron Microscopy........................... 383 Chemical Characterization of Surfaces..................... 386 Auger Electron Spectroscopy........................... 388 X-Ray Photoelectron Spectroscopy...................... 388 Time-of-Flight Secondary Ion Mass Spectrometry.......... 391 Application Examples.................................. 391 Example 1: Delamination of Polyester Insulation from Brass Cable Connectors............................. 393 Example 2: Printed Circuit Boards....................... 395 Example 3: Paint Delamination from a Molded Cabinet...... 402 Example 4: Delamination of a Surface-Mounted Integrated Circuit (IC) from a Solder Pad............... 402 Fracture and Fractography................................. 404 Structure and Behavior................................ 404 Crack Propagation................................... 407 Fractography........................................ 407 Case Studies........................................ 414 Fractography of Composites............................... 417 Interlaminar Fracture Features.......................... 417 Translaminar Fracture Features......................... 427 Conclusion......................................... 427 Reference Information................................... 431 Abbreviations and Symbols................................ 433 Index.................................................. 436 vi

ASM International is the society for materials engineers and scientists, a worldwide network dedicated to advancing industry, technology, and applications of metals and materials. ASM International, Materials Park, Ohio, USA This publication is copyright ASM International. All rights reserved. Publication title Product code Characterization and Failure Analysis of Plastics #06978G To order products from ASM International: Online Visit /bookstore Telephone 1-800-336-5152 (US) or 1-440-338-5151 (Outside US) Fax 1-440-338-4634 Mail Customer Service, ASM International 9639 Kinsman Rd, Materials Park, Ohio 44073-0002, USA Email CustomerService@asminternational.org In Europe In Japan American Technical Publishers Ltd. 27-29 Knowl Piece, Wilbury Way, Hitchin Hertfordshire SG4 0SX, United Kingdom Telephone: 01462 437933 (account holders), 01462 431525 (credit card) www.ameritech.co.uk Neutrino Inc. Takahashi Bldg., 44-3 Fuda 1-chome, Chofu-Shi, Tokyo 182 Japan Telephone: 81 (0) 424 84 5550 Terms of Use. This publication is being made available in PDF format as a benefit to members and customers of ASM International. You may download and print a copy of this publication for your personal use only. Other use and distribution is prohibited without the express written permission of ASM International. No warranties, express or implied, including, without limitation, warranties of merchantability or fitness for a particular purpose, are given in connection with this publication. Although this information is believed to be accurate by ASM, ASM cannot guarantee that favorable results will be obtained from the use of this publication alone. This publication is intended for use by persons having technical skill, at their sole discretion and risk. Since the conditions of product or material use are outside of ASM's control, ASM assumes no liability or obligation in connection with any use of this information. As with any material, evaluation of the material under end-use conditions prior to specification is essential. Therefore, specific testing under actual conditions is recommended. Nothing contained in this publication shall be construed as a grant of any right of manufacture, sale, use, or reproduction, in connection with any method, process, apparatus, product, composition, or system, whether or not covered by letters patent, copyright, or trademark, and nothing contained in this publication shall be construed as a defense against any alleged infringement of letters patent, copyright, or trademark, or as a defense against liability for such infringement.